给你来个现成的吧,不是偶写的,CoreJava上的例子:

程序代码：

/**
   @version 1.32 2004-05-05
   @author Cay Horstmann
*/

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Calculator
{
   public static void main(String[] args)
   {  
      CalculatorFrame frame = new CalculatorFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
   }
}
/**
   A frame with a calculator panel.
*/
class CalculatorFrame extends JFrame
{
   public CalculatorFrame()
   {
      setTitle(\"Calculator\");
      CalculatorPanel panel = new CalculatorPanel();
      add(panel);
      pack();
   }
}
/**
   A panel with calculator buttons and a result display.
*/
class CalculatorPanel extends JPanel
{  
   public CalculatorPanel()
   {  
      setLayout(new BorderLayout());
      result = 0;
      lastCommand = \"=\";
      start = true;
      
      // add the display
      display = new JButton(\"0\");
      display.setEnabled(false);
      add(display, BorderLayout.NORTH);
      
      ActionListener insert = new InsertAction();
      ActionListener command = new CommandAction();
      // add the buttons in a 4 x 4 grid
      panel = new JPanel();
      panel.setLayout(new GridLayout(4, 4));
      addButton(\"7\", insert);
      addButton(\"8\", insert);
      addButton(\"9\", insert);
      addButton(\"/\", command);
      addButton(\"4\", insert);
      addButton(\"5\", insert);
      addButton(\"6\", insert);
      addButton(\"*\", command);
      addButton(\"1\", insert);
      addButton(\"2\", insert);
      addButton(\"3\", insert);
      addButton(\"-\", command);
      addButton(\"0\", insert);
      addButton(\".\", insert);
      addButton(\"=\", command);
      addButton(\"+\", command);
      add(panel, BorderLayout.CENTER);
   }
   /**
      Adds a button to the center panel.
      @param label the button label
      @param listener the button listener
   */
   private void addButton(String label, ActionListener listener)
   {  
      JButton button = new JButton(label);
      button.addActionListener(listener);
      panel.add(button);
   }
   /**
      This action inserts the button action string to the
      end of the display text.
   */
   private class InsertAction implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         String input = event.getActionCommand();
         if (start) 
         {
            display.setText(\"\");
            start = false;
         }
         display.setText(display.getText() + input);
      }
   }
   /**
      This action executes the command that the button
      action string denotes.
   */
   private class CommandAction implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {  
         String command = event.getActionCommand();
         if (start)
         {  
            if (command.equals(\"-\")) 
            { 
               display.setText(command); 
               start = false; 
            }
            else 
               lastCommand = command;
         }
         else
         {  
            calculate(Double.parseDouble(display.getText()));
            lastCommand = command;
            start = true;
         }
      }
   }
   /**
      Carries out the pending calculation. 
      @param x the value to be accumulated with the prior result.
   */
   public void calculate(double x)
   {
      if (lastCommand.equals(\"+\")) result += x;
      else if (lastCommand.equals(\"-\")) result -= x;
      else if (lastCommand.equals(\"*\")) result *= x;
      else if (lastCommand.equals(\"/\")) result /= x;
      else if (lastCommand.equals(\"=\")) result = x;
      display.setText(\"\" + result);
   }
   
   private JButton display;
   private JPanel panel;
   private double result;
   private String lastCommand;
   private boolean start;
}